Ceramic materials are gaining a prominent position in dental applications, particularly in the restoration of crowns and occlusal surfaces. Wear of the restoration and the enamel opposing the ceramic restoration is often a key factor limiting the life of the restoration. However, the available data and information on wear performance of these materials are limited. Particularly, the effects of ceramic microstructure, oral environment, and machining on wear, and the wear behavior of natural enamel opposing the ceramic restoration, are not known. The objectives of this project are to determine the effect of microstructure on wear of dental ceramics and the opposing enamel, and to evaluate the possible effects of machining damage and environment on wear of selected dental ceramics. Six specific aims will be investigated: (1) determine the effect of microstructure on wear to define an optimum microstructure for best wear performance, (2) compare the microfracture wear mechanisms with the process of damage formation in fatigue and fracture and the material removal process in machining, (3) quantify the effects of machining damage (including surface roughness, surface integrity, and smear layers) on wear of selected dental ceramics, (4) evaluate the effect of environment (air, water, and artificial saliva) on wear of selected dental ceramics, (5) evaluate the effect of surface chemical tempering on wear of selected dental ceramics, and (6) examine wear of natural enamel tested against different ceramic microstructures in various environments. The results of this project will be instrumental in providing guidelines for selection and microstructural design of advanced dental restorative materials for an optimum performance based on wear of the restoration and the opposing natural enamel. An important issue in this research is the interplay between the effects of microstructure on wear, fatigue, and machining. Therefore, the microfracture processes involved in fatigue (Project 2) and machining (Project 1) will be compared with those observed for wear to develop some guidelines for establishing an optimum microstructure for best wear performance, without adversely affecting fatigue and machinability.